Measurement of albumin reflection coefficient with isolated rat glomeruli

Area of Science:

• Nephrology
• Renal Physiology
• Molecular Biology

Background:

• Macromolecular permeability of glomerular capillaries is crucial for kidney function.
• Increased permeability is associated with polycation treatment and renal injury.
• Previous studies showed isolated glomeruli respond to oncotic gradients.

Purpose of the Study:

• To investigate in vitro glomerular capillary permeability using isolated glomeruli.
• To quantify changes in albumin reflection coefficient (sigma albumin) and convectional permeability.
• To assess the impact of protamine on glomerular structure and permeability.

Main Methods:

• Isolated glomeruli from normal mammals were used.
• Glomeruli were treated with varying concentrations of protamine sulfate.
• Changes in glomerular volume in response to albumin gradients were measured.
• Scanning electron microscopy was used to examine podocyte morphology.

Main Results:

• Normal glomeruli exhibited an albumin reflection coefficient (sigma albumin) close to 1.
• Protamine treatment (600 µg/mL for 30 min) reduced sigma albumin to 0.2 ± 0.1.
• This reduction indicates a significant increase in convectional albumin permeability (0.8 ± 0.1).
• Electron microscopy revealed podocyte foot process retraction, fusion, and matrix denudation.

Conclusions:

• In vitro measurement of glomerular capillary permeability is feasible.
• Protamine sulfate significantly increases glomerular macromolecular permeability.
• Structural changes in podocytes correlate with increased permeability.
• This method allows for studying factors influencing glomerular injury.